An assembled tissue using four blocks. One block contains is cross shaped and contains cell stained green. The other three are rod shaped and have red stained cells. For reference the rods are 200 micrometers across. (Source: Ali Khademhosseini )

New research yields self-assembling tissues, paves the way for replacement organs

Tissue engineers like to dream big. They envision a world where one day a patient will donate a few cells and new, young healthy organs will be grown to replace ailing parts of the body. From appearance and athletic upgrades, through new integumentary tissues like skin, muscles, tendons, and ligaments, to essential organs, the technology may one day grant virtual immortality (though a brain transplant could be a curious proposition).

The engineers are aiming to start simple, regrowing commonly failing organs like the pancreas and kidneys. In order to build these more complex structures, scientists have to learn ways to build up from a cellular level.

Some of the first successful progress in this endeavor was announced by bioengineers at MIT and Harvard Medical School participating in groundbreaking new research. The engineers have created living blocks which they nickname living Legos, after the popular children's toy. These blocks consist of biofriendly shapable gels with living cells immersed within. These gels were shown in the research to be capable of shaping and producing advanced tissues similar to those found in organs.

He points to the liver, which is formed of repeating hexagonal lobes, which surround central blood vessels, providing blood filtration. While previous attempts have been made which "rely on the cells to self-assemble and re-create structures found in the body" by growing them on scaffolds in a top down approach, they have been relatively unsuccessful. Khademhosseini says the new method works from the bottom (cellular) up (to tissue level) and is much more promising as it works more like how the body grows organs in the first place.

His research is focused on carefully regulating tissue development from a cellular level by controlling a variety of factors. The cells used are suspended in polyethylene glycol, a biocompatible polymer. He pours the polymer/cell mix into tiny jello-like molds in shapes such as blocks, stars, spheres.

The molded polymers are then flashed with light to harden. The tiny structures measuring only hundreds of micrometers are then painstakingly pieced together. Once the smaller units are placed in contact they are glued together by more light hardening and the tissues begin to grow.

To help make the process easier scientist take advantage of the fact that the polymers are hydrophilic (water absorbing) by placing them first in water and then putting them in a bath of mineral oil, the oil pushes the little units together via hydrophobic effects, forming masses of branching tissue that can then start to grow and self assemble. Light hardens these masses, making sure they stay together. The shapes of tissue formed can be control by agitation of the oil and the shapes of the microunits.

The research findings were reported in the Proceedings of the National Academy of Sciences (PNAS) journal and can be found here.